Method and apparatus for moisturizing web material



Sep. 16, 1969 A. ARONSSQN ETAL 3,467,541

METHOD AND APPARATUS FOR MOISTURIZING wBB MATERIAL Filed June l5. 1966 3 Sheets-Sheet 1 www.

INVENTORSZ ARENT A BoNssoN ERIK ToRNQvls-r www* sept. 16, 1969 A. ARoNssoN :TAL 3,467,541

METHOD AND APPARATUS FOR MOISTURIZING WEB MATERIAL Filed June 15, 1966 FIGB.

5 Sheets-Sheet 2 INVENTORS'. ARENT ARONSSON BY ERIK T'RNQvxs-r W4? W ATTYS.

Sept. 16, 1969 A. ARONSSON ETAL 3,467,541

METHOD AND APPARATUS FOR MOISTUHIZING WEB MATERIAL Filed June 15, 1966 FIGB.

INVENTORS'. ARENT ARoNssoN BY ERIK TORNQUIST A'I'TYS.

United States Patent O U.S. Cl. 117-93.4 13 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a method and apparatus for conditioning a web of material, such as paper, and more particularly relates to a method and apparatus for uniformly moistening a web by subjecting the web to an electrostatic field and simultaneously therewith spraying a moistening agent such as water into the field and onto the web.

The novel method of the present invention includes the steps of providing anodic and cathodic elements respectively on either side of the web and spaced therefrom, and applying a potential difference between the electrodes so as to create an electrostatic field. Thereafter, the web is advanced through the electrostatic field and simultaneously therewith a moistening agent is sprayed into the electrostatic field onto the web. An important step of the method of the pres-ent invention is the supporting of the web between the electrodes so as not to touch the same while the web is passing therebetween.

The novel apparatus which is utilized for moistening the web material comprises means to supply the web spaced from means to receive the web, and means to supply an electrostatic field intermediate the web feed and receiving means. As is described in the body of the specification, the means to supply the electrostatic field includes cathodic elements which are spaced from the web along one planar surface thereof and anodic elements `which are spaced from the web along the opposite surface thereof and in such a relation with the cathodic elements to provide an electrostatic field therebetween. Means are also provided to prevent the web from contacting either of the elements, and means are additionally provided for supplying finely divided particles of a moistening agent into the electrostatic field and onto the web.

State of the prior art In most instances the manufacture and processing of lengths of webs made of animal or vegetable fibers, such as textile or paper webs, requires conditioning treatment. The conditioning treatment provided is primarily intended to give the web or sheetlike material properties making it capable of further processing or storage. For example, in manufacturing paper, moisture is usually applied to the web in order to raise and to equalize the water content throughout the length and width of the web. In this manner the dimensional stability of the paper is increased so that during subsequent storage, rolls and stacks of paper are prevented from absorbing moisture from the room air. As may be appreciated, absorption would normally take place in the peripheral portions of the roll or stacks which of course would result in a non-uniform moisture content and an uneven paper product.

Although the prior art is replete with apparatus for ice conditioning lengths of web or sheetlike material, these apparatus may be broken down into two groups practicing two distinct methods. The first method utilizes apparatus for spraying the web with finely distributed water particles to thus moisten the web while the second method utilizes large closed chambers having a high relative humidity which is absorbed by the web when the web is placed in the chamber. Of course in the spraying method, difficulties are encountered with respect to obtaining a uniform distribution across the surface of the web, while conditioning the web in moist air according to the second method requires expensive and bulky equipment.

A more recent method of conditioning a web utilizes an electrostatic field. In this method, the web is moved over and in contact with a stationary or movable electrically potentialed element. The field is formed in this type of apparatus between the potentialed element and a plurality of emission or cathodic electrodes connected to a high potential D.C. source. In the apparatus of this type, water is supplied in a finely distributed form and attracted to the web by the electrostatic field. It was found that the presence of the electrostatic field increases the quantity of moisture per unit of time which may be applied to the web as opposed to either of the two abovementioned methods. It has been theorized that the primary reason for the superiority of the electrostatic method is that the water particles, due to the emission from the cathodic or emission electrodes, are charged or ionized and are attracted by the electrostatic force field to the anodic or collecting electrode. The effect of the emission or electrostatic field is observable in processing plants where the potential between the cathodic and anodic elements is switched on and off. For example, after a high potential is applied between the anodic and cathodic electrodes, a high density mist is observed which is substantially confined to the encompassing area between the anode and cathode. Upon switching off the potential, on the other hand, the mist appears to transform into a diffuse cloud having no limited boundaries and thus filling large parts of the environment.

It has been discovered, however, that there is a distinct disadvantage to providing an electrostatic field in the manner as above outlined. This disadvantage relates to non-uniformity in the distribution of the moistening agent across the surface of the Iweb which has been found to be due to the contact between the web and the anodic electrode. Thus if the contact causes more moistening agent to wet one portion of the web than another portion, a greater electrical conductivity will be exhibited at these points than at the other points in contact with the anodic electrode. In this manner, the lines of force in the electrostatic field become deformed about this point and attempt to pass through the higher or more conductive region thereby supplying more Water to the already highly moistened point.

Description of the invention It is a principal object of the present invention to provide a novel method and apparatus utilizing the principles of electrostatic field moistening while improving the distribution of the moistening agent across the web.

Another object of the invention is to provide means for preventing the removal of the electric charge from the web portion exposed to the moistening agent during the period it is exposed to the spray.

Still another object of the present invention is to provide means for preventing contact between the lweb and the anodic or cathodic elements as it is being subjected to the spraying action.

Still another object of the present invention is to provide specially designed anodic and cathodic electrodes whereby all of the charged moistening agent particles arriving at the web carry a charge of the same polarity in order that any point on the web reached by a charged particle will repel a like charged particle and that particle will attempt to find a non-wetted point on the web.

Another object of the present invention is to provide at least one substantially planar potentialed element in order to achieve a more homogeneous electrostatic field.

Another object of the present invention is to provide, in conjunction with one of the electrodes, blowing apparatus which prevents the web `from moving against the anodic electrodes and simultaneously therewith is humidified so as to prevent the surface being blown against from becoming dry.

Another object of the present invention is to provide means for correcting a non-uniform moisture content in a web exhibiting a non-uniform moisture prole transversely of the web.

Other objects and a fuller understanding of the invention may be had by referring to the following specification and claims taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic, fragmentary, side elevational view of novel apparatus constructed in accordance with the present invention and illustrating the novel method of the present invention;

FIG. 2 is an enlarged fragmentary sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken along line 3-3 of FIG. l;

FIG. 4 is an enlarged fragmentary sectional view taken along line 4-4 of FIG. 3;

FIG. 5 is a schematic, fragmentary plan view, similar to the View of FIG. 2 but illustrating a different embodiment of a portion of the apparatus of the present invention;

FIG. 6 is a fragmentary schematic plan view showing another embodiment of apparatus constructed in accordance with the present invention;

FIG. 7 is a schematic, enlarged fragmentary sectional view of another embodiment constructed in accordance with the present invention; and

FIG. 8 is an enlarged sectional view taken along line 8 8 of FIG. 7.

Referring now to the drawings, and especially FIG. 1, apparatus 10 for moistening a web or sheetlike material 11 having low conductive properties, is illustrated therein. The web 11 is supplied to the apparatus 10 by supply means, in the present instance a supply roll 12, and is received on the outlet side of the apparatus by receiving means or a take-up roll 13. As schematically shown in FIG. 1, rolls 14-1-9 serve to guide and tension the web as it passes through the apparatus 10. In the present instance the web is drawn through the apparatus by a drive roll connected to drive means comprising an electric motor 21. Intermediate the web supply and receiving rolls is means, designated generally 30 for purposes of identification, to provide an electrostatic field through which the web 11 passes in its travel from the supply means to the receiving means. In addition, moistening means 50 is provided to supply a wetting or moistening agent, such as water, into the electrostatic field as the web 11 passes therethrough. It should be noted that two identical means '30 to supply an electrostatic iield and two identical means 50 to supply a moistening agent are illustrated in FIG. l in order to insure full and uniform moistening of the web, identical parts being given identical numbers. However it should be recognized that in some instances only a single means 30 to provide an electrostatic field and a single means 50 to supply a moistening agent are necessary in order to attain a proper moistening of the web.

.4 In order to provide an electrostatic field, cathodic or emission and anodic or collector elements are positioned on opposite sides of the web respectively and a D.C. p0- tential is applied between the elements. To this end, and as best shown in FIGS. 1 and 3, a plurality of emission electrodes 31 are positioned substantially transverse to the direction of travel of the web 11 and supported by insulators 33 connected to a portion of the frame 22 of the apparatus 10. In the present instance, each of the emission electrodes comprises a nozzle 34 (see FIG. 4) having coaxial conduits 35 and 36 therein which merge at the tip 37 of the nozzle, for purposes which will become evident hereinafter. As illustrated in FIG. 4, the outer conduit 35 communicates with an inlet 38 connected through suitable piping 38a to air supply means 39, while a second inlet 40 communicating with the inner conduit 36, is connected through suitable piping 40a to a moistening agent supply means 51. As is discussed hereinafter, the air flowing through the conduit 35 causes an ejector effect at the nozzle tip 37 with the moistening agent contained in the supply means 51, causing the moistening agent to flow therefrom as a mist. A stem 41, coaxially mounted in the inner conduit 36, acts to control by rotation of a handwheel 41a, the amount of water ejected from the nozzle.

On the other side of the web 11 is the anodic element, in the present instance and as best shown in FIGS. 1 and 2, including a plurality of blow boxes 42 which act as a common collector. Although the term collector is in some senses a misnomer, i.e. because it does not really collect, the term is used hereinafter to indicate the electrode or electrodes potentialled oppositely to the emission electrodes. As shown in FIG. 2 the blow boxes extend transversely of the web 11 and are spaced from one another in the longitudinal direction of travel of the web so as to define exhaust ports or openings 43 therebetween. In addition, each of the blow boxes 42 contains a plurality of apertures 44, the purpose of which is explained hereinbelow. As shown schematically in FIG. l, one side of a D.C. power source or supply 45 is connected via a switch 46 to the emission electrodes 31, the other side of the source being grounded and connected to the blow boxes 42, or common collector electrodes. As the D.C. source potential applied between the electrodes is extremely high, for example on the order of 100,000 volts D.C., the emission electrodes are preferably made negative and the collector electrodes are grounded to reduce for the operator the risk of flash-over or the like from the electrodes to ground.

It should be recognized that the spacing between the electrodes and the web should be sufficient to prevent arcing or flash-over when water or the like is being sprayed upon the web. For example, with a potential of approximately 100,000 volts D.C., the spacing between the web and the tip 37 of the nozzles 34, or electrodes 31, should be on the order of 7 inches (in a direction perpendicular to the web as shown in FIG. 1) while the spacing between the web and the collector electrodes should be about lo of an inch.

To aid in preventing contact of the web with the collector electrodes, and in accordance with a feature of the invention, a supply of treated gaseous medium, such as air, is preferably provided to the blow -boxes which, through the apertures 44 maintains the web 11 a small distance from the collector electrodes. To this end, the blow boxes 42 are connected via a duct 70 to gaseous medium supply means, in the present instance comprising a blower 71. As illustrated, conditioning means are provided, in the present instance on the inlet side of the blower, to prepare the gaseous medium and prevent inadvertent drying out of the web as it passes over the blow boxes 42. As shown in FIG. l, the means may include consecutively positioned elements such as a filter 72, a heater 73, a moistening device 74 (to add a percentage of moisture to the gaseous medium), and a de-watering grate 75 (which serves to remove large particles of water from the gaseous medium prior to its entry into the suction side of the blower '71). Various #blowing devices such Sas above-described may be utilized to prevent the web 11 from touching the collector electrodes, for example the devices shown in the United States patents to Wallin et al. Nos. 3,231,165 and 3,272,415. It is noteworthy that the stability of the web is improved if the apertures 44 are designed so that the gaseous medium emanating therefrom is given a component substantially parallel to the plane of the web, whether in the direction of travel or opposite thereto.

As the moistening agent commonly used is water, and as in the embodiment illustrated in PIG. l the nozzles 34 acting as emission electrodes 31 are connected to the high potential power source, the supply means for providing the moistening agent or water requires a special design to prevent the water supply line from becoming hot with respect to ground. As best illustrated in FIG. 1, the moistening agent supply means 51 comprises a nozzle supply tank 52 supported by a portion of the machine frame 22 via insulators 53, and preferably positioned below the horizontal level of the nozzles to prevent a positive head from 'being placed thereon. Cascading apparatus 54, including an intermediate tank 55 also connected to the frame 22 by insulators 56, is positioned above the tank 52 and includes a valving arrangement such that when water is being supplied to the intermediate tank 55 from a water supply source 57, no water will be supplied to the supply tank 52. Alternatively, means must be provided for preventing water flow from the supply means 57 into the intermediate tank 55 when the intermediate tank is filling the nozzle supply Itank 52. To this end, the intermediate tank 55 includes a solenoid actuated dumping valve 58 controlled by a switch-type float level 59 located in the supply tank 52. In a like manner, a second solenoid actuated valve 60 located in the water supply source 57, also connects a switch-type float level 61 in the intermediate tank 55. As is common with this type of arrangement, upon the contacts closing, for example in switch level 59, the solenoid associated with the valve 58 will be actuated, permitting water to dump from the sluice tank into the supply tank 52. The valve 60, of course, is actuated in a like manner from the switch-type float level 61. To prevent actuation of the valve 60 when the valve 58 is open, or vice versa, each of the actuator lines from the levels is fitted with a solenoid-operated, normally-closed switch 62 which opens the other circuit upon one of the valves being actuated, thus permitting actuation of only one valve at a Itime and thereby preventing the water supply line from ever becoming hot with respect to ground. It should be recognized that the valve yarrangement may be wholly mechanical by a simple insulated mechanical cross connection of the valves so that only one or the other of the valves is opened at any one time.

As from time to time the nozzles 34 my jam due to dirt or the like collecting in the nozzle, it is preferable that a drip pan 64 be provided beneath the nozzle in the event any charged water particles fall thereon.

In the embodiment of the present invention illustrated in FIG. l, the paper or web 11 which is to be conditioned is mounted as shown on the supply roll 12. Thereafter the web is threaded mechanically or by hand through the apparatus into the receiving means or take-up roll 13. Air from the air supply means 39 is then provided to the nozzles 34 and the switch 46 associated with the D.C. power source 45 is closed. In this manner, an electrostatic eld is formed between the emission electrodes 31 and the collector electrodes comprising the blow boxes 42. As illustrated in FIG. 4, the tips 37 of the nozzles are provided with a pointed portion through which the ejector action of the air flow causes water flow. About the tip, the field intensity becomes very high giving a corona discharge effect which causes ionization of the surrounding gas, the positive ions or particles being attracted to the nozzles 34 while the negative ions or particles being attracted toward the collector electrodes or blow boxes 42. Because of the density of the -air-water mist or mixture around the nozzle, the water particles sprayed out collide with negative ions or particles and are thereby given a negative charge, the water particles thus charged are thereby attracted by the collector electrodes but are deposited on their way thereto in the intermediate web.

Where the paper is not saturated with water, it has a high resistivity. For example, an uncoated and dry paper weighing approximately grams per square meter has a resistance of 1012 ohms per meter width/meter length at a 5% moisture ratio, and a resistance of l09 ohms per meter width/meter length at a 10% moisture ratio. The effect of the high resistivity is that the charge carried by a water particle onto and into the paper does not spread very quickly through conductivity in the plane of the paper. Thus if the surface of the paper does not contact any electrically conductive object, such as the collector electrodes, the surface can store charges in the water particles at the point in which they arrive at the surface. As these particles have a like charge to subsequent particles being sprayed onto the surface of the material, they repel the subsequent particles causing them to find areas not previously met by prior water particles. In this manner, and in accordance with the invention, a more uniform moisture distribution is obtainable.

As illustrated in FIG. 1, either for subsequent or further treatment, or for take-up on the take-up roll, it is preferable that means Ibe provided to remove the charge from the web after it has passed through the electrostatic field. To this end, the rolls 17 and 19 may be grounded thus conducting the charge away.

In certain instances the web to be treated will exhibit, prior to treatment, an uneven moisture content profile in the transverse direction of the web. In this event, it is desirable to provide means operative in conjunction with the means 30 for providing the electrostatic field, to ad just the amount of moisture applied transversely of the web To this end, the collector electrodes may be arranged as shown in FIG. 5 wherein longitudinally extending transversely spaced surfaces 42a separated by intermediate spaces 44a are each connected via switches 45 separately to ground. In this manner, it is possible to selectively strengthen and weaken the electrostatic eld in specific areas transversely of the web and thus effect the quantity of the water particles attracted to selected portions of the web.

The adjustment of the electrostatic field can be irnproved by dividing either or both the emission and col lecting electrodes into a plurality of separate elements insulated from one another. For example the collecting electrodes shown in either FIG. 2 or FIG. 5 may be used with the emission electrodes 131 shown in FIG. 6. For example as illustrated in FIG. 6, pairs of emission electrodes 131 may be switched in and out as by switches 132, thus connecting and disconnecting, where and when desirable, a power supply 145, similar to the power supply 45 previously described. In this manner almost any desired v-ariation of the field intensity yacross the width of the web may be obtained.

The uniformity of distribution as a result obtainable from any of the afore-mentioned embodiments is dependent to some extent upon the water particle size and the uniformity in the size of such particles which can be achieved. In this connection, it has been found that the electrostatic field has a pronounced favorable effect and gives water particles which are smaller in size and thus more easily absorbed by the web, than the water particles which may be obtained by spraying without an electrostatic field. The reason for this is not absolutely clear, but it is theorized that the decrease in particle size is due to the unipolar charge of the water particles which prevents the agglomeration of the particles between the nozzles and the web. In certain instances the effect may be accented by reducing the surface tension of the particles, such as by heating the water or mixing it with a surface tension reducing agent.

With certain paper it may not be particularly beneficial or desirable to provide very small water droplets. In such an instance the apparatus may be modified by interposing between the web and the nozzles a wire mesh screen or grid, such as the screen 150 illustrated in FIG. 7. Preferably the screen should extend parallel to the surface of the collector electrodes 151 and be spaced a distance from the web suicicnt to prevent arcing or flashover. As illustrated in FIG. 7, collector electrodes 151, similar to the blow boxes 42 heretofore described, and the screen 150 are connected to opposite sides of a power supply 151, similar to the power supplies 145 and 45 above-described. However, as before, a plurality of nozzles 152 arranged transversely of the web may be used to supply water into the web through the screen mesh. One of the advantages of this arrangement is that the nozzles need not be electrically insulated from ground thus eliminating the complexities of the cascading arrangement described with reference to FIG. l.

It should be noted that when treating very thick webs such as cardboard webs, it may be desirable after spraying and treatment in the apparatus 10 to allow the water to penetrate further into the web and to be distributed therein by passing he web a plurality of times between a plurality of guide rolls in a closed chamber with a relatively high humidity. ln this manner the moistening agent or water is given sufficient time to permeate the relatively thick web.

Thus the present invention provides a novel method and apparatus utilizing the principles of electrostatic field moistening while substantially improving the distribution of the moistening agent across or transverse to the web.

We claim:

1. A method of applying moisture to a web or sheetlike material, comprising the steps of: providing anodic and cathodic elements on opposite sides of said web and spaced therefrom, applying a potential difference between said elements so as to create an electrostatic field therebetween, advancing said web through said electrostatic field and simultaneously therewith spraying at least the portion of said web in said field with finely distributed particles of a moistening agent, supporting said web between said elements by blowing a gaseous medium against one surface of said web to support the same so as not to touch the elements while passing therebetween, and providing a variable intensity in said electrostatic field transversely of said web.

2. A method in accordance with clairn 1 including the step of conditioning said gaseous medium by imparting moisture to said gaseous medium prior to blowing it against the web.

3. A method in accordance with claim 1, wherein said blowing step includes the step of imparting to said gaseous medium as it is blown against said one surface, a component substantially parallel to said surface to thereby improve the stability of said web as it passes through said field.

4. A method in accordance with claim 1 wherein at least one of said anodic and cathodic elements comprises separate electrodes positioned transversely of said web, and including the step of selectively switching at least one of said electrodes out of said applied potential to thereby provide said variable field intensity transversely of said web.

5. A method of applying moisture to a web or sheetlike material, comprising the steps of: providing anodic and cathodic elements on opposite sides of said web and spaced therefrom, applying a potential difference between said elements so as to create an electrostatic field therebetween, advancing said web through said electrostatic field and simultaneously therewith spraying at least the portion of said web in said field with finely distributed particles of a moistening agent, supporting said web between said elements by blowing a gaseous medium against one surface of said web to support the same so as not to touch the elements while passing therebetween, and conditioning said gaseous medium prior to its blowing against the surface of said web by imparting moisture to said gaseous medium.

I6. Apparatus for moistening a web-like material comprising: means defining a path of travel for said web-like material, means to supply an electrostatic field comprising at least one cathodic element spaced from said path on one side thereof, at least one anodic element spaced from said path on the opposite side thereof and in such a relation to said cathodic element to provide an electrostatic field therebetween upon application of a potential between said elements, means to prevent said web-like material from contacting said elements, and means for supplying finely divided particles of moistening agent into said electrostatic field on said one side, said anodic element comprising a plurality of blow boxes, each having an apertured planar surface substantially parallel to the web path and gaseous supply means to blow gaseous medium through said apertured surface onto one surface of the web, said blow boxes being laterally spaced from one another to define discharge ports therebetween for exhausting said gaseous medium from said one web surface.

7. Apparatus according to claim 6 wherein each of said blow boxes is coextensive with the width of said path, said discharge ports providing a fiow component along the length of said path.

8. Apparatus according to claim 6 wherein each of said blow boxes extends along the length of said path and is insulated from the others, and including switching means for applying potential selectively to said boxes to afford variations in the electrostatic field intensity across the width of said path.

9. Apparatus in accordance with claim 6 including conditioning means in said gaseous medium supply means to impart moisture to said gaseous medium.

10. Apparatus for moistening a web-like material comprising: means defining a path of travel for said material, means to supply an electrostatic field comprising at least one cathodic element spaced from said path and positioned on one side thereof, at least one anodic element spaced from said path and positioned on the opposite side thereof and in such a relation to said cathodic element to provide an electrostatic field therebetween upon application of a potential between said elements, means to prevent said web-like material from contacting said elements, and means for supplying finely divided particles of moistening agent into said electrostatic field on said one side, said anodic element including a plurality of planar surfaces insulated one from the other and lying closely-spaced across the width of said path, and switching means to afford selective connection and disconnection of said surfaces with the potential to thereby afford variation of the intensity of said field across the width of said path.

11. Apparatus for moistening a web-like material comprising: means defining a path of travel for said material, means to supply an electrostatic field comprising at least one cathodic element comprising a nozzle spaced from said path and positioned on one side thereof, at least one grounded anodic element spaced from said path and positioned on the opposite side thereof and in such a relation to said cathodic element to provide an electrostatic field therebetween upon application of a negative potential to said cathodic element, means to prevent said web-like material from contacting said elements, and means for supplying finely divided particles of water into said electrostatic field through said nozzle including cascading apparatus comprising a supply tank connected to said nozzles, an intermediate tank electrically insulated from said supply tank, a supply line electrically insulated from both of said tanks, and valve means to effect ow alternatively from said supply line to said intermediate tank and from said intermediate tank to said supply tanks.

12. Apparatus in accordance with claim 11 wherein said nozzle comprises coaxial conduits merging into a tip, and air supply means connected to one of said conduits, said supply tank being connected to the other of said conduits `and being positioned below the level of said nozzle.

13. Apparatus in accordance with claim 11 including a plurality of cathodic elements, each comprising a nozzle, wherein said nozzles are insulated one from the other and including switch means intermediate at least some of said nozzles and said potential to afford selective connection and disconnection of said nozzles into said eld.

References Cited UNITED STATES PATENTS 10 ALFRED L. LEAVITT, Primary Examiner J. H. NEWSOME, Assistant Examiner U.S. C1. X.R. 

